Two principal families of flying craft guidance systems exist.
The first family encompasses autoguidance systems in which the flying craft is capable, by itself, of steering towards an objective. These autonomous systems customarily implement onboard inertial means, associated with a laser or infrared electromagnetic designation assembly pointed in the direction of the objective. In such a case, the volume and weight of the onboard electronics is appreciable and directly impacts the cost of the craft.
The second family encompasses guidance systems remotely controlled from a fixed ground installation, or from an installation onboard a ground vehicle or an installation which is likewise airborne. These systems customarily use an active or passive probe capable of locating the flying craft with respect to the objective. It is beneficial in this case to use radar techniques in active or passive mode, this technique allowing “all weather” operation.
The active radar mode is, however, difficult to use when the equivalent cross-sectional area of the flying craft to be guided is small. Moreover, this mode does not allow direct identification of the target. This is why the use of a passive mode based on an emitter onboard the flying craft is preferred, the said craft then being located by a ground system or one which is itself onboard a vehicle. However, when the craft flies at an altitude of a few decimeters or a few meters, elevational location turns out to be very tricky because of the signal reflections off the ground. Moreover, location may also be disturbed in the horizontal plane by lateral reflections off surrounding objects such as for example buildings. Moreover, an onboard emitter does not make it possible to measure the distance traversed if it does not have a responder function. If a responder function is implemented at the level of the emitter, the cost and volume of the electronics onboard the flying craft grow appreciably.
When the flying craft spins, it may be beneficial to know the angle of roll at each instant, to guarantee effective guidance. This information is not accessible with conventional systems, be it within the framework of autoguided systems or systems guided from a fixed ground installation or one which is itself onboard a terrestrial or airborne vehicle.